An ECC99 as an SRPP at about 15mA standing current driving a Sowter 8665 headphone transformer would do the job. A Sowter 10K:10K bridging transformer on the input, such as the 3293, will give you your balanced input.

Currently listening to a 6U10 or 6ac10's-Mosfet hybrid headphone amp.
6u10 is an input gain stage and SRPP second stage with a Mosfet follow output. I did allow for feedback from the output to the input of the SRPP stage. The output is cap coupled.
I was looking for a simple, inexpensive amp that could use what stuff I had on hand.
The tubes will be visible though a window in the front of the amp, the idea is to use 304 mirror finish to make a divider to reflect the light forward and hide the circuitry. I used foil glued to cardboard for a mock up...

An ECC99 as an SRPP at about 15mA standing current driving a Sowter 8665 headphone transformer would do the job. A Sowter 10K:10K bridging transformer on the input, such as the 3293, will give you your balanced input.

Looking to stay away from transformers unless its for power...

Quote:

Originally Posted by roline

Currently listening to a 6U10 or 6ac10's-Mosfet hybrid headphone amp.
6u10 is an input gain stage and SRPP second stage with a Mosfet follow output. I did allow for feedback from the output to the input of the SRPP stage. The output is cap coupled.

Mosfet having the same trans-conductance, "voltage in, current out" as a tube and in a Class A follower application has the advantage of low output impedance over a tube....
I tried other ideas, came back to this one. The 6U10 is not the most ideal low voltage tube, but the results are impressive. Other ideas included 5 watt tube PP and SE circuits, but the transformers are very expen$ive for the bandwidth.
You might try a SRPP with a set of GU50's or KT88's